Process for the manufacture of high alpha-cellulose fiber



Patented Sept. 14, 1926.

UNITED STATES- PATENT Mme,

enonen A..BIOHTER .mn umron 0. serum, or isnnrm, NEW mmmn, A8-

srenons'ro BROWN courm, or BERLIN, nnw mmrsmnn, A conrom'rron or MAINE.

PROCESS-FOB THE MANUFACTURE OF HIGH ALPHA-GELLUIOSE'IIBEB.

' No Drawing. I

This invention relates to the Ipireparationof high alpha-cellulose fiber. gh alplliizcellulose fiber may be produced by coo g unbleached pulp with an alkaline cooking liquor,-a caustic soda solution being espe cially adapted for" this purpose,--and then bleaching the cooked product. This cooking may take place in digesters at any suitable temperature and pressure, although ingen- 10 eral it has been found more economical and expedient to'cook in open tanks under atmospheric pressure. The alkali in solution reacts with and dissolves the lignin and the less resistant beta and gamma celluloses of the pulp so that when the liquor is drawn off after the necessary periodbf digestion, the resultant product after bleachin is very white and contains about 94% alpa-cellulose fiber. High alpha-cellulose may be em- .20 ployed as a substitute for cotton fiber in paper-making, in the preparation of the cellulose esters, the cellulose ethers, and

other compounds which require the use ofsubstantially pure cellulose. A drawback to 5 the use of caustic soda as the alkaline di- .gesting-agen't, however, is thatit renders the process expensive. The objectof this invention is to provide a more economical method for the preparation of a high alpha-cellulose so fiber, yieldmg a product which shall possess the same characteristics as those obtained by the use of caustic soda.

Briefly, this object is attained by treating the unbleached pulp with an oxidizing agent and then' cooking' the treated pulp in a caustic lime solution. Other advantages are 1 obtained by this invention, which will be subsequently pointed out. p I

The use of lime in cooking-liquors is old,

40. of course, but the characteristics required of ahlgh alpha-cellulose pulp are net realizedin the product obtained from an'ordinary lime treatment of the usualcellulosic ma terials, and so far as we know, the treatment of pulp with lime in the manner employed by us is new.

. If a milk of lime cooking liquor were substituted for a caustic soda solution-under. the same tlm'e, pressure, and temperaturecondil tions as in the treatment of unbleached pulp for the preparation of a high alpha-cellulose Appflcation filed April 9, 1925. Serial m. 21,962.

fiber, the product obtained thereb would be 'much more diflicult to bleach wit out excessive quantities of bleachin 1 agent. This is perhaps due to the fact t at slaked lime, which is a weak base and only slightly soluble in water in comparison with caustic soda imparts a much lower alkalinity to on and retained by the fiber. Hence the lignin and other coloring matter present in the pulp are, in accordance with our process, sub ected to a preliminary treatment that renders these undesirable substances more easily and more completely removable by the milk of lime cooking liquor, so that fiber of pure whiteness may subsequently be obtained with a small quantity of bleach. Without such preliminary conditioning of the fiber, inasmuch as the colorin substances are not. sufiiciently removed y the lime digestion, in' order to produce aproduct of the desired color it would otherwise be necessary that excessive bleach be used in the bIeaching operation, with the-result that- 'oxy-cellulose, and thefiber strength would be materially afiected by the excess bleach. The extent of reaction between the relatively weak alkali and the coloring substances of the unbleached fiber may be m-- creased by the use of a high temperature and pressure in the digestion, but this would complicate the process and call for the use of comparatively intricate apparatus, and might prove to be as ex ensive as a direct caustic soda treatment, inot even moreex+ pensive;

It hasbeen found that the necessity for. the use/of exc'essivebleach, may be avoided by treatment (if the fiber beiore the lime digestion with a small quantity of oxidizi other coloring matters, rendering these more susceptible to the action of the lime cooking liquor. It is important that only a small quantity of oxidizing agent be used in the preliminary treatment, for if the pulp is sensibly bleached by the oxidizing agent, the alpha-cellulose content of the final prod uct will be low and'the pulp not so well suited as a substitute for cottonfiber in papermakin or. for conversion intogcellulose esters. %he reaction with a small quantity of oxidizing agent, as for example, chlorine, is a selective one,the more .lgesistant alipha-cellulose apparently being unafiecte ,and is very rapid, the chlorine uniting with the coloring substances within a few' minutes at room-temperature.

The pretreated pulp is then subjected to the action of a lime cooking liquor and is boiled under conditions similar to those employed in the caustic soda solution process as hereinbefore v described, where an open tank may be used.

The beta and gamma cellulose constituents and the coloring substances contained in the pulp are removed therefrom by reaction with theflime in solution, fresh lime from the milk of lime going into solution as the dissolved lime is consumed in the reaction. The liine is effective in the removal of beta and gamma celluloses and also reacts with the coloring matter and reaction-products resulting from the chlorine treatment. The

resulting p product is equal in quality to that obtaine by a direct caustic soda solution cook, and requires about the same small quantity of bleach to produce a very white,

high-alpha cellulose stock.

' Another important advantage may be obtained by usin the chlorine pretreatment process, which 1s that the wood chips may be slightly undercooked in the digesters, re sulting in a longer fiber, The pulp thus produced would ordinarily be more difl'icult to bleach, owing to the fact that it contains a higher-per cent of lignin; but the quantity of oxidizing agent used in the pretreatment may be increased so as to react with the additional amount of lignin resulting from undercookingl The pre-treated pulp is then subjected to the 'lime cooking-' solution and upon bleaching yields a very whitealpha-cellulose fiber. of high tear test,

folding endurance; and bursting strength.

Thus by the use of chlorine as a pre- The chlorine reacts with and formsv aeoaaee treating agent, caustic soda may be replaced by lime to afford a more economical method of producing high alpha-cellulose pulp of equally good quality and without the use of special ap aratus.

A spec1 c example of the foregoing proc- V ess is approximately as follows:' After wood chips havecbeen digested in a suitable sulphite liquor, for example Ca(HSO lIqIIOI', the digester contents are blown (slightly undercooked if so desired) and the sulphite pulp washed, screened and delivered to the open digesting tanks. The pulp is treated in the tanks at a stockdensity of about 5% and at room-temperature with a chlorine solution containing 0.3% to 1.5% chlorine based on the weight of the fiber, the chlorine reacting with and being consumed by the ligneous matter in the pulp within a few minutes. The pulp is now washed clear of reactionproducts,

and is squeezed to a stock-density of, say,

16%., then is transferred to the cooking tanks, and milk of lime added until a 10% pulp suspension is obtained, there being present about 6% to 9% reactive calcium oxide, based upon the bone-dry fiber weight. The suspension is brought to about 200 to 212 F. by blowing live steam into the open. tanks, and is thoroughly agitated at this temperature from five to eight hours, depending upon the characteristics of the particular sulphite pulp undergoing digestion. The less resistant beta and gamma celluloses and the reactive li other coloring matter react w1th and are efi'ectivelyremoved from the pulp by the lime. After the digestion, the stock is washed clear of the reaction products in the usual manner. The stock leaving the cooking tankshas approximately the following characteristics Alpha cellulose 94+% Fiber length 0.91.1'mm.- Copper number.. 1.4-2.0.

eous and chlorine solution, without loss in alphacellulose content.

While the -process herein described may be practiced in the treatment of unbleached -pul' produced by either an alkaline or an aci digestion, it may be employed to great advantage in the treatment of unbleached sulphite pulp to produce a high yield of fiber characterized by a very hlgh percentage of alpha or resistant cellulose, and by a pure white color,,as indicated by the spe'-- ,cific example herein given.

We do not herein claim the subject matter 2. The process of producing high alpha-' cellulose fiber from sulphite pulp, which comprises treating said pulp with a chlorine solution to remove or render more reactive a part of the lignin and other coloring matter, and cooking said pulp in a lime cooking liquor to remove beta and gamma celluloses and more ligneous matter therefrom.

3. The process of producing a high alphacellulose fiber from sulphite pulp, which comprises treating said pulp with a chlorine solution containing-chlorine equal to 0.3% to 1.5% of the weight of the pulp to remoye or render more reactive part of the lignin, and cooking said pulp in a lime cooking-liquor to remove beta and gamma cellulosses and more lignin therefrom.

4. The process of producing a high alphacellulose fiber from suphite pulp, which comprises slightly undercooking chips in a sultained from said sulphite digestion with a chlorine" solution to remove or render more reactive part of the lignin, and cooking said pulp in a lime cooking liquor to remove the less stable beta and gamma celluloses and more lignin therefrom.

5. The process of producing high alphacellulose fiber from sulphite pulp, which comprises treating said pulp with a chlorine solution to remove or render more reactive part of the lignin, cooking said pulp in a lime cooking-liquor to remove the unstable. celluloses and more ligneous matter therefrom, and bleaching the cooked pulp.

6. The process of producin a superbleached high alpha-cellulose fiber, which comprises subjecting unbleached sulphite pulp to a preliminary oxidizing reaction, cooking with milk of lime, separating the pulp from soluble reaction products, bleaching it with calcium hydrochlorite solution and superbleaching it with a chlorine solution.

In testimony whereof we signatures.

have aflixed our GEORGE A. RICHTER. MILTON O. SGHUR.

phite cooking liquor, treating the pulp ob- 

